Effect of Low Temperature Carburising on the Corrosion and Mechanical Behaviour of AISI 304 Austenitic Stainless Steel after Hydrogen Charging

The hydrogen fuel cell is one of the most promising power source as it is clean, efficient and sustainable. Many metallic components exposed to hydrogen in such systems are made from austenitic stainless steels. This research evaluates the effect of hydrogen on the mechanical and corrosion properties of an commercial austenitic stainless steel with and without the low temperature carburizing (LTC) process S³P feat. Kolsterising®. In addition to an improved wear resistance due to the interstitial embedding of carbon, which leads to a significant increase in surface hardness, this study explores the feasibility to protect austenitic stainless steel parts from hydrogen embrittlement.

The stainless steel investigated was AISI 304 in solution annealed (SA) and cold worked (CW) conditions. Hydrogen was introduced into the materials by means of cathodic electrochemical charging in 0.2 mol/L H₂SO₄ + 1 g/L Na₂HAsSO₄ at 80°C for 72 hours. Tensile tests were performed to examine the mechanical properties including both total elongation and area reduction. Open circuit potential (OCP) testing and potentiodynamic polarization were employed to evaluate the corrosion resistance in 3.5 wt.% NaCl solution.

For cold worked 304 (304 CW), the LTC-treatment improves the resistance to hydrogen embrittlement significantly. In the solution annealed condition, hydrogen embrittlement susceptibility was improved slightly by LTC-treatment. Hydrogen charging reduces OCP, corrosion potential and breakdown potential of the specimens to a certain extend. However, the impact is less with LTC compared to the samples without this treatment, in general.

Based on these results, examples from different hydrogen applications are shown that can benefit from this surface engineering approach to achieve a more sustainable material resistance.